Interpretive Summary: Production of U.S. ethanol is produced at a rate of more than 9.3 billion gallons per year; an additional 4.4 billion gallon capacity is under construction. Methods that can be used to further optimize the amount of ethanol from a bushel of corn promise to have a large effect on the amount of ethanol produced and on the economics for producing ethanol. This paper details a laboratory scaled protocol that predicts the amount of ethanol that can be produced from a sample of corn. Furthermore, the method only makes use of equipment commonly available in most laboratories. It is envisioned that this method will be of use for comparing corn hybrids for ethanol yield and for modeling process changes. A procedure to predict hybrid potential would benefit corn seed companies, corn producers, and ethanol processors.

Technical Abstract:
Production of U.S. ethanol is produced at a rate of more than 9.3 billion gallons per year; an additional 4.4 billion gallon capacity is under construction. Kernel composition and wet milling properties are not correlated with ethanol yield. A procedure to predict hybrid potential would benefit corn seed companies, corn producers, and ethanol processors. The objective was to develop a laboratory procedure to measure ethanol yield from corn samples and evaluate the developed procedure for accuracy and precision. To determine parameters for routine analyses, effects of mill type, dry solids, and yeast addition were investigated separately followed by studying combined effects of fermentation time (Tf), glucoamylase dose, and yeast addition. Measurement of ethanol using high performance liquid chromatography (HPLC) and gravimetric (change in weight due to CO2 loss) methods were compared. Using the procedure developed, ethanol yields for five diverse hybrids (dent, waxy, white, high oil, and high amylose) were measured. Effects of mill type, dry solids, Tf, glucoamylase dose, and yeast addition were found to be significant (P<0.05). The gravimetric method estimated higher yields (2.87±0.07 gal/bu) than HPLC (2.72±0.1 gal/bu) and had a higher level of precision. Both methods had variations of <4% relative to their respective means and gave similar conclusions. In the final procedure, we used corn (25 g batch) liquefied with alpha amylase (60 min at 90°C) in 75 mL distilled water and simultaneously saccharified and fermented (64 hr at 32°C) with glucoamylase and yeast. The method detected differences in ethanol yield for the five hybrids (1.06 to 2.92 gal/bu). The method is suitable for routine testing of ethanol yield potential and as a reference method for verifying more rapid measurement techniques.